The present inventors invented an apparatus for generating X-rays by placing a hemimorphic crystal, for example a lithium niobate (LiNbO3) single crystal, which is known as a pyroelectric crystal, in a vacuum of approximately 3 Pa to 6 Pa or a low gas pressure atmosphere, periodically changing the temperature of this crystal so that charged particles, including electrons are generated on the surface of the crystal because the particles that cannot follow the offset of the charge on the surface collide with a target or a hemimorphic crystal, and thus, generating X-rays (Japanese Patent Application No. 2003-407985 and Japanese Patent Application No. 2004-98371), and invented an apparatus for generating ozone by radiating X-rays into an air flow including oxygen through a beryllium window or the like (Japanese Patent Application No. 2004-99069).
Furthermore, the present inventors invented an apparatus for generating ozone more efficiently by using strong X-rays generated through bremsstrahlung from an X-ray target where an electron gun for generating thermoelectrons is provided together with a hemimorphic crystal within a vacuum housing as described above so that the thermoelectrons from this electron gun are directed so as to collide with the target using a high electrical field generated through the change in the temperature of the crystal (Japanese Patent Application No. 2005-94742).    (Patent Document 1) Japanese Patent Application No. 2003-407985    (Patent Document 2) Japanese Patent Application No. 2004-98371    (Patent Document 3) Japanese Patent Application No. 2004-99069    (Patent Document 4) Japanese Patent Application No. 2005-94742